Microfluidics refers to devices and methods for controlling and manipulating fluid flows at length scales less than a millimeter. Miniaturization of a laboratory to a small device, usually termed as lab-on-a-chip, is an advanced technology that integrates a microfluidic system including channels, mixers, reservoirs, pumps and valves on a micro scale chip and can manipulate very small sample volumes of fluids. While several flow control concepts for microfluidic devices have been developed to date, here flow control concepts based on thermally responsive polymer solutions are presented. In particular, flow control concepts base on the thermally triggered reversible phase change of aqueous solutions of the polymer Pluronic will be discussed. Selective heating of small regions of microfluidic channels, which leads to localized gel formation in these channels and reversible channel blockage, will be used to control a membrane valve that controls flow in a separate channel. This new technology will allow generating inexpensive portable bioanalysis tools where microvalve actuation occurs simply through heaters at a constant pressure source without a need for large external pressure control systems as is currently the case. Furthermore, a concept for controlled cross-channel transport of particles and potentially cells is presented that relies on the continuous regeneration of a gel wall at the diffusive interface of two co-streaming fluids in a microfluidic channel.

A computer-controlled microfluidic extensional flow device is developed for trapping and manipulating micron-sized hard and soft particles. The extensional flow is generated in a diamond-shaped cross-slot that has each corner connected to a pressure-controlled liquid reservoir. By employing an imaging-based control algorithm, a particle can be made to move to an arbitrary position within the slot by adjusting the reservoir pressures and hence the fluid flow rates into/out of the slot. Thus, a soft particle can be trapped indefinitely at a point within the slot, and a known hydrodynamic force can be applied to study the dynamics of stretching and breakup of the particle. Alternatively, adhesion or coalescence dynamics of soft particles may be investigated by effecting a controlled collision between two particles. The device is validated by measuring the low interfacial tension of a compatibilized oil-water interface.

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No description available.

A computer-controlled microfluidic extensional flow device is developed for trapping and manipulating micron-sized hard and soft particles. The extensional flow is generated in a diamond-shaped cross-slot that has each corner connected to a pressure-controlled liquid reservoir. By employing an imaging-based control algorithm, a particle can be made to move to an arbitrary position within the slot by adjusting the reservoir pressures and hence the fluid flow rates into/out of the slot. Thus, a soft particle can be trapped indefinitely at a point within the slot, and a known hydrodynamic force can be applied to study the dynamics of stretching and breakup of the particle. Alternatively, adhesion or coalescence dynamics of soft particles may be investigated by effecting a controlled collision between two particles. The device is validated by measuring the low interfacial tension of a compatibilized oil-water interface.

Thesis (Ph. D.)--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references (p. 168-174).

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 78-81).

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 61-63). Also available on the World Wide Web.

Micro-devices are developed for uses in targeted drug delivery and microscale manipulation. Here we numerically and analytically study two promising devices in early stages of development. Firstly, we study Armoured Microbubbles (AMBs) which can self-propel as artificial microswimmers or facilitate microfluidic mixing in a channel when held stationary on a wall. Secondly, we study an artificial cilium, which due to its unique design, when placed in an array, easily produces a metachronal wave for fluid transportation. The Armoured Microbubble was designed by our experimental collaborators (group of Philippe Marmottant, University Grenoble Alpes) and consists of a partial hollow sphere, inside which a bubble is caught. Under ultrasound the bubble oscillates, generating a streaming flow in the surrounding fluid and producing a net force. Motivated by the AMB but considering initially a general setup, using matched asymptotic expansions we calculate the streaming flow around a spherical body undergoing arbitrary, but known, small-amplitude surface shape oscillations. We then specialise back to the AMB and consider its excitation under ultrasound, using a potential flow model with mixed boundary conditions, to identify the resonant frequencies and mode shapes, including the dependence of the resonance on the AMB shape parameters. Returning to our general streaming model, we applied the mixed boundary conditions directly to this model, calculating the streaming around the AMB, in good agreement with experiments. Using hydrodynamic images and linear superposition, this model was extended to incorporate one wall, and AMB compounds. We then study the streaming flows generated by arrays of AMBs in confined channels, by modelling each AMB as its leading order behaviour (with corrections where required) and superposing the individual flow fields of all the AMBs. We identified the importance of two confining walls on the streaming flow around the array, and compared these flows to experiments in five cases. Motivated by this setup, we theoretically considered the extension of a two fluid interface passing through an AMB array to quickly identify good AMB arrays for mixing. We then studied the second artificial micro-device: an artificial cilium. Tsumori et. al. produced a cilium of PDMS containing aligned ferromagnetic filings, which beat under a rotating magnetic field. We modelled a similar cilium but assumed paramagnetic filings, using a force model balancing elastic, magnetic and hydrodynamic forces identifying the cilium beat pattern. This agreed with our equilibrium model and asymptotic analysis. We then successfully identified that the cilium applies the most force to the surrounding fluid at an intermediate value of the two dimensionless numbers quantifying the dynamics.

Doctor of Philosophy / Department of Chemistry / Christopher T. Culbertson / My doctoral dissertation consists of three fundamental studies: 1) synthesis of biocompatible materials that can be used as microfluidic substrates, 2) characterizing these materials with respect to properties important to microfluidic fabrication, biochemical separations and concentration enrichment, and 3) employing these novel devices for real world applications in bioanalytical chemistry. The surface properties of a substrate will dramatically affect the resolution and efficiency that can be obtained for a specific CE separation. Thus, the ability to modify the surface is very useful in tailoring a microfluidic chip to a specific separation mode. The substrates we have synthesized for microfluidic devices include metal oxide modified poly(dimethylsiloxane) (PDMS), poly(ethyleneoxide)-PDMS (PEO-PDMS) coblock polymers, and surfactant coated PDMS. The metal oxide modified PDMS materials we synthesized include silica-PDMS, titania-PDMS, vanadia-PDMS and zirconia-PDMS. The surfaces of these materials were characterized using contact angle, X-ray photoelectron spectroscopy (XPS), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electroosmotic mobility (EOM) measurements. All of the metal oxide modified PDMS surfaces were significantly more hydrophilic than native PDMS, suggesting potential application in separations of biopolymers. In addition to being more hydrophilic the EOF and zeta potential of the channels were stable and quite durable with aging. Well characterized silane chemistry was used to derivitize the surface of the PDMS metal oxide surfaces allowing a number of different functionalities to be placed on the surface. This method has the potential for wide applicability in many different fields, but specifically for the fabrication of microstructures that need specific surface chemistries. We have also made a number of advancements using sol-gel chemistry and laminar flow within microfluidic channels to fabricate nanoporous membranes. Sol-gel patterned membranes are a simple and facile method of incorporating nanoscale diameter channels within a microfluidic manifold. These membranes have been used to perform preconcentration of amino acids, proteins and small particles for further analysis and separation using CE. We are also using these membranes for further study in desilanization and protein recrystallization studies.